1. Field of the Invention
This invention relates generally to the field of digital data communications over digital telecommunications lines. More particularly, this invention relates to a method and apparatus for transmission of byte-organized data to a receiving station that may employ byte boundries different than those of the transmitting station. For example, the present invention may be used for disabling an echo canceller in a long distance telephone line used for data communication.
2. Background of the Invention
Echo cancellers are frequently used in long distance telephone lines such as those provided by U.S. SPRINT Corp. and other long distance carriers to improve the intelligibility of voice communications. Echoes are caused by mismatches in impedance (generally at hybrid transformers) coupled with delays. Although it is desirable to eliminate these in voice communication, the presence of an echo canceller in a bit-synchronous digital network results in numerous data errors.
U.S. Pat. No. 4,945,533 and U.S. Pat. No. 4,881,221 both describe a method and apparatus for disabling the echo canceller by sequentially transmitting all possible variations of a signal used to disable the echo canceller for each possible byte alignment of the network during a call setup period. These patents are hereby incorporated by reference.
The present invention provides a systematic method and apparatus to solve the problem of disabling the echo canceller by determining the proper alignment to the byte boundaries of the digital network and transmitting a predetermined signal with the proper byte boundaries to disable the echo canceller. The present invention can also be used in communicating with the network for, for example, control purposes when such communications are required to be aligned with byte boundries.